sir737
As I far as I understand it (I did try and get my TRE to sign it) only someone who could conduct the IR-SPA-SE skill test can sign for the credit based on EASA FCL annex 8.
A better explanation is that I use the credit of my MP type rating to have my IR-SP-SE revalidated by experience, rather than test.
Under EASA still only an IRE or a CRE/SE with IRR privelages can revalidated your IR-SPA-SE
The CAA a few years ago answered an e-mail stating a TRE cannot revalidated a single pilot IR unless he is also IRE or CRE IRR.
But as BOSE X says there are some discrepencies on how things are done with the cross crediting. If they allow now it would great to know
Regards and Merry Christmas