Numbers corruption

A maintain a large spreadsheet of my Pins and other like information.

when opened I find that about the first 20% of the sheet is corrupted by an overprint in smaller type from elsewhere in the sheet.

Considered reverting to earlier version as suggested in various help pages, but this means that I will lose the last update(s) to the sheet.

This problem occurred once before but only the first few rows were affected and I simply ignored the problem.

Any guidance would be much appreciated