I must assume from all the above that the GA of the fuselage, D.4395, was issued, without amendments in 1945, not 1943.

Also from all the above whether or not the photo at the start of this thread shows two or just one escape hatch is irrelevant. I accept that the aircraft is PA474. To reach the state shown in the photo, the mid-upper turret had first to be removed and then re-placed. Also a substantial test rig on the fuselage top had been installed and later removed. With all these alterations the fuselage top and the absence of a rear hatch cannot represent a production aircraft.

Let me review my argument from Avro design documentation.

Slots cut out of frames for stringers 2a, 2, 1, 2, 2a
Stringers are symmetric about aircraft centre line, stringer 1 is on centre line.

Frame 19, D.3153 last amended 15-3-45, has these slots
Frame 18, D.3153 last amended 14-3-45, has these slots.
Frame 17, D.3152 last amended 15-3-45, has these slots.
Frame 16, D.3151 last amended 14-3-45, has these slots.
Frame 15, D.3150 last amended 20-5-42, has these slots.
Frame 14, D.3149 last amended 27-1-42, has these slots.
Frame 13, D.3148 last amended 31-5-44, has these slots
Frame 12, D.2973 last amended 10-5-45, Transport Joint, all stringers terminated, no slots
Frame 11, D.3146 last amended 9-11-45, has these slots

Frame 10, D.3145 last amended 29-4-45, DOES NOT have these slots
Frame 9, D.3144 last amended 15-7-45, DOES NOT have these slots

Frame 8, D.3143 last amended 15-4-49, has these slots except 2a
Frame 7, D.3142 last amended 17-5-44, has these slots except 2a
Frame 6, D.2973 last amended 10-5-45, Transport Joint, all stringers terminated, no slots

The GA of the fuselage, D.4395, shows auxiliary stringer 2a to be fitted only between frames 12 and 16
It also shows the front escape hatch (or as Avro calls it Emergency Exit) between frames 9 and 10
This hatch is mounted horizontally on stringer 3 both sides as well as the two frames.

The distance between the rear of frame 9 to front of frame 10, is 18 27/32″, this being the length front to back of the front hatch.

If a rear hatch were fitted, most likely it would be between frames 16 to 17 or 17 to 18.
But in both locations stringers 2, 1, 2 are shown fitted and continuous.
In addition the distances between both frames 16 to 17 and 17 to 18 are just 15 1/8″.
So either a rear hatch if fitted is some 3″, 20%, shorter than the front one or the position of one of the frames is adjusted..
I would imagine that both these two possibilities are most unlikely.
Moreover, the stringers 2, 1, 2 are shown to be continuous throughout frames 12 to 19.
They would have to have been shown as deleted in the location of the rear hatch.

So the conclusion from the above documentation is that all Lancasters built after the issued amendments had only one escape hatch along the top of the centre fuselage, not two as shown by PA474 in its current state.

My questions remain unfortunately. Did all Lancasters built before mid 1945 have two escape hatches?
Did all Lancasters built after mid 1945 have just one hatch?

I would need ro know that there is no contradictory photographic evidence to be sure. Can anyone help with this? That is with a photo of a production Lanc built before mid 1945 with just one escape hatch. And with a photo of a production Lanc built after mid 1945 showing two hatches.

How many Lancs were built after mid 1945 anyway?

Many, many thanks to all of you for your help.
My very best wishes to you all
Mike

Ok, it looks as though I am wrong. Internet says PA474 was issued to 617 squadron to replace aircraft lost in Chastise. So it was issued some time in late May or in June 1943. So PA474, the aircraft shown here was built probably in the first half of 1943.

Now, when were the Lincoln-like extended rudder trims installed? And wasn’t the aircraft used for trials with a vertical wing or similar stuck on its back and at that time lacked the nid-upper turret. Later, in the mists of mental fog I think a mid-upper turret was obtained from Argentina where they had stopped operating Lancs not long before.

So I’m getting near now to what I wanted; the removal of the trials vertical airfoil/wing and installation of the turret required a re-building of a major part of the top decking of the fuselage.

Someone, several years ago, complained in some forum or other of the shoddy mis-aligned riveting visible along the fuselage top from the astrodome. It was not shoddy work, but a major and successful re-working of the top fuselage between aft of the astrodome to the mid-upper turret location.

Oh, the joy of digging out old memories.
Mike