Thank you p45cal. My first PQ solution involved 2 queries, yours is just 1. I will open and see on Monday how you did it.
Please help me understand the step by step process so I could apply it to the actual data. Where did the Table (CurrentYearRegistration) that was merged to the Source come from?
3 pm: I was able to follow through the steps until the fnLastReg. The error message says that the PQ is of lower version. Google says I must update my Excel to later version than 2013 but travel restriction is still in effect in this part of the planet.

Often when you get the warning that you have an earlier version of Power Query than what the workbook was developed in you can just dismiss the warning and carry on. However, I attached a diagnostic version of fnLastReg which I'd like you to go in as if to edit it and select the steps one by one until it complains, then tell me which step it complained at and what the error message says. I might be able to write a work-around.
Link to picture:
Image at Box

ps. The CurrentYearRegistration is just your table filtered for the current year and all but the Registration number columns removed.

Attached Files

Diagnosticmsofficeforums45701Registration.xlsx (22.0 KB, 7 views)

Thanks p45cal. I just finished going through all the steps and ended up with the same result. I felt so overwhelmed. I will try them in the actual data and see how they behave.