We play stolen bid doubles. So if over caller intervenes, what is your reason saying 2/1 is off?
A: "Stolen Bid Doubles” are used when we open 1NT and they overcall. So, 1NT and a 2D overcall -- Double is a transfer to hearts.
Personally, I don’t use or teach them – but regardless, they have nothing to do with 2/1 GF (since it was a 1NT opening).
I do like the "Stolen Bid Double" for a 2C overcall however and you can read more about how to handle this and other 1NT overcalls here.
As to auctions where we open a SUIT and they overcall, double would be a negative double (not “stolen bid”).
If you respond on the 2-level (after their overcall), it shows 10+. Yes, you might have 13. But, you need to be able to bid your suit with 10, 11 or 12 – since 1NT is no longer available as forcing (or semi-forcing). So, I open 1H, they overcall 1S and you bid 2C. That is natural and 10+ HCP (not GF).
Hope this makes sense...