What's The Scoop On Giving Toddler Formula To Infants?
In light of the formula shortage and the “do’s and don’t” lists coming out by major organizations, I want to take a second to go through the evidence of some of the most recent statements so that you can understand where their decision comes from, but more importantly, so you have the information you need to make a decision that is in the best interest of your family. While big organizations get to live in a space of hypotheticals, parents can’t. You understand that there is a difference between optimal and necessary, and sometimes your top few options aren’t available.
When you are faced with moving down the list away from the things you want, you often run into choices that simply became necessary, and as a parent, it can feel terrifying making those choices for your baby.
So, with this in mind, what is the scoop on using a toddler formula for an infant, if other options aren’t available?
In the US, the FDA regulates Infant Formula and Toddler Formula differently. The regulation for infant formula is more regulated. The FDA does not ‘approve’ of any formula, but they do control distribution of those products in the US. In order to be commercially marketed in the US an an infant formula, it must meet specific criteria.
The criteria that the FDA sets out for infant formula have parameters for:

Minimum and Maximum Nutrient Composition.
Those requirements can be found here. These are the nutrient levels that in the FDA has established for infants under the age of one. 
Specific labeling requirements.
The FDA has very specific labeling requirements for infant formula, and when a formula manufacturer does not meet those standards, the formula will be recalled. Here is an example of a recall due to a labeling challenge, which had absolutely nothing to do with the appropriateness or safety of the product for most babies. These formulas are used extensively (and safely) in Europe. They are simply missing a statement about insufficient iron for infants which could potentially impact a very small subset of infants.

Infant formula manufacturing has specific and strict quality control requirements for tracking ingredients and for maintaining safety throughout the manufacturing processes.
This allows production to be able to be tracked and halted if there is a problem, and helps to ensure adequate safety is taken to make sure that infant formula is safe during manufacturing. The FDA inspects infant formula manufacturing plants yearly as well. Many formula manufacturers who make infant formulas also make toddler formulas, and they are likely made them at the same manufacturing plant with the same ingredients. 
Specific Language requirements
Infant formulas must meet certain language requirements on the label, and have more stringent language regarding their marketing as a breastmilk substitute. Toddler formula is marketed to infants over the age of 12 months, and doesn’t have the same labelling, language and marketing requirements as infant formula. Toddler is also not necessary, but that’s not the point of this post. Language requirements are very specific for infant formula. Toddler formula has much more leeway.
For example, toddler formulas will state that they are made to meet the standards of a growing toddler, but there are no established standards for commercial milk product for toddlers. Infant formula can not make claims that aren’t backed by evidence.
What you can do is compare the toddler ingredients to the ingredients found on the link above, and see if the formula meets all the safety requirements for infant formula. If it does, then from a purely nutritional point of view, the FDA’s own metric tells you that is is nutritionally appropriate product for a baby less than 12 months old, and the formula would not pose a health risk, based on the nutrient composition alone.
From a public health perspective, since infant formulas are more closely regulated, as a whole, that makes them safer for infants. Being able to determine if a toddler formula meets the nutrient requirements requires some extra work and investigation. There is a lot of places for miscalculations and potential error.
Because SOME toddler formulas are not nutritionally appropriate does not make ALL toddler formulas unsafe for infants. And because it isn’t as regulated, it may have other things that could increase the risk factor. But we are in this situation because of a recall about safety concerns in an infant formula. So, while it is true that there are risk associated with toddler formula, it isn’t true that there is zero risk associated with infant formula.
If you have questions about an individual brand of toddler formula, then you can usually call the company and ask, if you have time. This is definitely true for smaller, more boutique brands. They are almost always happy respond. You want to ask them specifically if their product meets the nutritional values for infant formula, and ask for documentation.
Kabrita Goat Milk Toddler Formula is an example of a toddler formula that meets the nutritional safety standards for infants. Another infant formula that meets the nutritional composition is “Nature’s Only Gentle Toddler Formula”. The can doesn’t show linoleic acid, but their internal documents do.
I haven’t gone through a list of toddler formulas that meet the vitamin standards for infant milk, and I’ll keep adding to this list as I come across them.
At the end of the day, you are the one with the baby at home, being faced with decisions that may not be your first, second or third choice. If you’ve moved down your ‘best options’ list, and your baby isn’t brand new or medically fragile, you might have a few more options. Only you should get to decide which choices are best for your family, and deserve the information to be able to do exactly that.