Hetchins didn't always do the repairs on the frames which were taken into their shop. This applies to both Tottenham and Southend. They often used other builders to do repairs for them. You have to remember that the majority of their earlier frames which were owned and ridden by real cyclists would have their old fashioned and dated fork ends replaced with modern Campagnolo ones, inevitably whilst this replacement was being carried out the rear triangle was re-spaced for modern 5 or 6 speed blocks and probably the original number was not put on. So please don't get bogged down in minutia regarding an H missing of the frame number etc. This ain't no big deal. Most of the older Hetchins I saw racing from the 60's through to the 1980's mostly had non-original front forks and modern rear dropouts, possibly without any numbers extant. And how about the original ones with no number present?
Thats all for now. Keep those wheels spinning, in your memories if not still on the road. Be lucky Mick Butler Huntingdon UK.