Found in Wikipedia
"During production of the first batch of 100 Tempest V "Series Is", distinguishable by their serial number prefix JNxxx, several improvements were progressively introduced and were used from the outset on all succeeding Tempest V "Series 2s", with serial number prefixes EJ, NV and SN. The fuselage/empennage joint originally featured 20 external reinforcing "fishplates", similar to those fitted to the Typhoon, but it was not long before the rear fuselage was strengthened and, with the fishplates no longer being needed, the rear fuselage became detachable."
https://en.wikipedia.org/wiki/Hawker_Tempest#cite_note-Bentley_1973,_pp._92-93.-31
I remember seeing something in a post on britmodeller but can't seem to find it right now.
Craig