Tag Definitions (109 vs. 115 and 76 vs. 128)

Imported from previous forum

When 3rd party transactions are involved, there are session level tags which are similar to application message level tags.

1st: For tag 109 and 115, can they have different values or should they be the same value. If different, does one override the other? If so, which takes precedence?

2nd: Same question for tags 76 and 128.

Thanks for the help.