So don’t think any reputable business is going to not take steps to secure the data or to delete it after validating it.
Reputable businesses fail to delete or secure data all.the.time.
It's just something people and organisations are crap at.
Even when they've made a token gesture towards it, they frequently haven't deleted or secured all copies, which multiply unintentionally especially as emails get pinged hither and yon still carrying the attachment.
I've just had this with a hospital clinic which I hesitantly entrusted with an emailed medical form. I was replied to by a different person with my medical form still attached – dreadful practice. So that form is now in my sent box, my inbox, and at least two people in the clinic's email boxes, and possibly devices they're reading emails on if sometimes they do admin from home. I can trawl through manually finding and deleting it in my boxes... but not theirs.
And that's if they're even aware of GDPR requirements in the first place.
The number of times I've had to explain to my local council that they do not need my date of birth... They might want it, because they're all about Big Data and what uses they might come up with for data they've previously collected and combined across multiple databases... but THAT IN ITSELF is a breach of data protection legislation, which states that subjects must give informed consent for each purpose for which their data is processed, and that you can't just collect personal data speculatively in case it comes in handy later. I've had the call operators wail "But there's a space on my form for DoB!"
Yeah, no.
I was particularly annoyed by the council because mostly it's been an entirely unjustified collection of data – outright breach of GDPR – but on the one occasion my age had any relevance at all they could have proportionately met their aim by the trad method of asking my age group, 21-25, 26-30, etc. Not asking for my exact birthday which my bank uses as part of my security id.
Honestly, the argument "It's important, so they can't possibly be doing it wrong," does not hold any water whatsoever.