Different language variants in MultiTerm: how do they work in practice?

Some of the termbases I created in MT contain the en-UK variant, while most agency projects are actually defaulted to en-US. After some research, changing this particular piece of data within the termbase seems like quite a hassle. I decided to run a little test and the "UK" database works just fine for an US-English project.

 The question is: is it always the case? And, is there any other way the UK-US difference could cause a malfunction in any of my translation projects, or should I just keep the en-UK termbases in their original shape instead of revamping everything/starting a new termbase from scratch? Is there a safe "umbrella" variant incorporating all variants, or would "international English" be treated as a separate variant?

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