Column A contains the New ID number.
Column B contains the Old ID number.
In many cases, there are several New ID numbers for one repeated Old ID number.
And several repeated Old ID number for one New ID number.
There are a several long lists of Old ID from different files that need to be matched to New ID.
The concept is that a list of Old ID could be pasted into Column F, and column E could repeat the same Old ID as often as it appears in Column B with the matching New ID from Column A, shown in column D - manual example shown in file.
Hope this makes sense.