Hi Peter,
Just to add some final detail in case anyone else comes across this with the same issue... Updating past API v201702 requires minimum version 0.24 of the google-api-ads-ruby gem, but that version removes support for p12 key files for service accounts, yet we were using them. (The issue wasn't related to any other gems in the end). So we've been forced to change how we do oauth2 authentication or else our adwords processing will stop working. It's now done, and wasn't actually too bad in the end.
I appreciate the specifics of this relate to ruby gems and not just the pure adwords API itself, but I do think that the frequency that we're forced to update the API is very poor. There should be no reason to force API users to have to upgrade that frequently. I appreciate you may want to continuously tweak functionality and fix issues, but try looking at how vendors like Stripe manage their API. Their older versions still function perfectly well. Yes, if we want to use new functionality then of course an upgrade would be necessary. But if not, we should be able to continue using older versions of the API near-indefinitely without them being disabled.