I love this kind of thing. Modern rarities that no one is bothered about because there is little financial incentive to look, they involve a little effort to understand and spot and because they haven't been exposed in the Sun or on dodgy click-bait tabloid websites. I hate that side of decimal collecting, plus all of the deliberate misleading crap and even fakes on eBay over the years.... remember the dateless mule 20p, when people were actually grinding off the date of normal ones and attempting to pass them off as 'dateless'!
How many 2006 10p's do you think you've actually seen in total? 2006 was a massive mintage at 118m+, so it would seem the type A die(s) were for whatever reason, just used for a tiny fraction of that total. Even if it was for a million coins, it's still under 1% of the 2006 total. All these years later and finding a stunning example will be very hard (as you know!), like finding a decent 1807 slave trade £2 with no DG initials (i.e. the circ only variant).
They may well be rarer than the Kew 50p. Might even be comparable with the mule 2016 £1 coin with the tiny 2017 dates on the reverse - and surely more of those should exist in the wild but a magnifying glass is needed to even see it.