Let’s play devil’s advocate for a moment!
What’s the purpose in migrating? If all you need is a list of properties for comparable purposes, would a simple print-out from your current software in PDF format suffice?
PDF files are searchable so an “archive property list” could be easily filtered to show just the data you want. Create everyone a copy and you’ve achieved what you need.
If you want to defend against Trading Standards or legal challenges, would having details of the details sent to Mr Smith on a long withdrawn property really help you?
If you decide not to migrate, this would give you a “fresh start” – the chance to save corrupting your lovely new system with lots of old data and the chance to make sure your properties are perfectly entered. Even if we migrate your properties, you’ll still need to spend a couple of minutes on each one cleaning up things that we haven’t been able to migrate (often the type, style, location – there is sometimes the need to add a PDF or an EPC, etc). It is probably no more than 5 minutes to enter a property from scratch.
There’s a way of taking care of applicants too. Just send them an email from your old system with a link to your new registration form. Explain that you are installing a wonderful new system and ask them to re-register.
Not convinced you? Never mind! We’re always happy to migrate data as long as you understand the “it can never be perfect unless we spend weeks on it” caveat.