@LeanneS I need to start thinking about how we identify these matches - when does the next file come through. If I can get the most recent file I'll start asking questions

SO I looked at the s/sheet & analysed the first few & see that in general they don't have emails but I'm finding

1. Contact for whom there is a single match in CiviCRM based on first name + last name + street address + city + postal code. This seems like the easiest & we can merge them civicrm/contact/view?reset=1&cid=490772
2. Contact for whom there is a single match in CiviCRM based on first name + last name + email (same as #1)
3. Contact has multiple matches based on the above. Option 1 - throw an exception & have someone go through & merge - probably after the first import this might be improved & perhaps then we would loosen to Option 2 - merge to the most recent contact who has source - 'check' civicrm/contact/view?reset=1&cid=19960248
4. Contact has limited info - ie. just name + multiple matches based on that. IF ONLY 1 has source - 'check' acivicrm/contact/view?reset=1&cid=25885358
5. variants on limited info - how little must there be?

I'm thinking about adding an 'Engage Strict' import that will reject ones it's not sure about matching while we hone our rules. We can easily pick off the ones that meet criteria we have decided on & then focus on others. This means we will get some pretty easily

General note - we seem to be able to identify engage donors in 2 ways 1) source=check 2) already has a donation of type Engage. At this stage I'm using the former but the latter is an option. Hmm - would not work for civicrm/contact/view?reset=1&cid=427095

So what I'll do here is a first iteration that does 1 & throws an exception for no match & put it on staging & then try the import against it (with the file from @LeanneS & then I'll iterate on that. Even if we stop after the first iteration we will be getting some of them.