We can have a tendency to underplay what we have done. Often in tech we pull amazing rabbits out of hats - and then when people say how great it is, we'll respond with how it was nothing and anyone could have done it. It's nothing special...

Someone gave me some advice a few years back which was - if you don't feel mildly embarrassed when you read your CV you are probably underselling yourself.

On the reaching out to old employers - unless you left on really bad terms - drop them a line. You are a known quantity, it's a low effort hire that won't cost them anything (apart from your salary).