Unique ID AA AB AC...AAA-> create a new UNID for unique entry.

Hello,

Im working on a document that ultimately, will have new data input into it. As such, I've created unique IDs in one tab and then another tab where data will be entered and if there is already an ID for this and then return that ID.

This is tab 1- the UNID generator. In my spreadsheet it goes all the way down to BOE. so A, B, C,... AA, AB, AC.... AAA, AAB,....ABA etc BOE
All these letters are values, I used a concatenation to get the values as quick as possible but ultimately copy and pasted them as values after (initially I did not intend on data being added)

Tab 2- Here we have a data sheet, new companies will be added here.
=INDEX('UNID Generator'!B:B,MATCH(@A:A,'UNID Generator'!A:A,0)) This is the formulae used in the second column to find the UNIDs for each company
What im looking to do is essentially make it such that when company 18 through 27 are input on the data sheet (Tab 2) it will add the company and  create a new UNID on the UNID generator sheet.

I'd also like to note I havent used numbers because this is a unique ID for another field.