Nogin,
That's not my understanding. With an IR, converting to JAA WILL carry over your ATPL credits, with an extended validity of 7 years from your IR pass. This is a rolling 7 years too, so each time you renew the IR, you get another7 years.
What makes you think that the credits do not carry over? That was the info PPRuNe and Gatwick gave me, so I'm curios why you think diferently. Maybe it has something to do with number of hours maybe? (I'm over 1300)
Do it nicely.
PS