What is a Google taxonomy version?

What a new version can change

A new release can add categories, remove them, or move them. Google’s statement that it translates older values means an old ID in your feed is not simply dropped — but the category it lands on after translation is Google’s decision. If a category you use was split, you may prefer to choose the new, more specific entry yourself.

Keeping stored IDs current

Keep the version date next to the IDs you store. When Google publishes a new file, compare the two and re-check only the rows whose category changed. The category index states the version it was built from, so what you read there matches what you would send.

How SellerSort tracks the version

The tools read one stored snapshot of the taxonomy file, and the category pages name that snapshot. When Google publishes a new release, the new file is fetched alongside the old one and the two are compared entry by entry — added, removed and renamed categories — before the site switches over. Nothing changes under a stored ID without that comparison being run first.

For your own data the same idea works at any scale: keep the date of the file you chose from next to the IDs, and when the date changes, re-check only the rows whose category appears in the list of changes.