Index or Last Occurrence Formula

Hello,

This is my first post, I hope I am doing this correctly and I hope this is not written in a too confusing way. I am using excel to help setup syntax for IBM SPSS and need to know how to find the last occurrence of a string that has a slight change at the end of every cell. Ultimately the SPSS syntax should look like below using the QS2 set which as 16 sub variables.

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My issue is every set of questions has a different number of variables and I only need the 1st and last occurrence of a set (ie.Q2S.1 to QS2.16 whereas the QS3 series only has 11 so it would be Q3S.1 to QS2.11).

Attached is a sample workbook I have started to set up, any assistance would be greatly appreciated, I believe it is an index formula that I need but I am not sure...

Thank you! It worked great