For international comparisons, preserve the original currency and date rather than repeatedly converting old observations at today’s rate. Conversion can be added for presentation while the underlying entry remains intact.
A simple spreadsheet is enough initially. One row per observation, one column per known fact, and blanks where information is unavailable. Avoid filling gaps with confident guesses.
When was the last increase, and what does the tenancy agreement say about rent reviews? Also, are there unresolved maintenance items? The right process and notice depend on the tenancy and how the increase is agreed, so I would establish those points before choosing a number. Discussing an...
I would cap the gap rather than waive the valuation condition completely. €34,500 is already meaningful exposure, so the contract should make clear what happens if the valuation misses by more than that amount. Also, is this money separate from your repair reserve and deposit? If the same cash...