Say I have a simple string like "License". In one case, it's a driving license and in another it's the license plate of a car. I can add comments so that it gets translated properly. But, my translation vendor is saying that, in the future the strings might get changed as the TM will see that there are 2 translations for this string and possibly apply the wrong one in the future. 

Some background:

We send full files, so, 99%+ of the strings are not new. But we send them all, expecting to get back previous translations for old strings and leveraged/manual translations for the new ones. We do  not expect old strings to flip between different possibilities every time we re-submit them. But, since the TM does not record the context (the context being the ID of the string), but rather just records the English (source) and the translated strings, having a source with 2 different translations means the TM could pick either translation and thus change strings that we are already set on. 

Our vendor is not using Trados.

Are my expectations reasonable? Do I need a new vendor or does the vendor need a better TM? Or, is this reality correct - you cannot have the same source string with 2 different translations as the TM does not record the context?