When was the code written?
What do we have that could point us in the right direction? The code page and micro writing to start with, according to one report the back of this book had been torn off which could mean that the impressions left were from the original writing done on the real back of the book. Here's the thing, the process for agents using secret writing techniques was to write the code or message on one piece of paper possibly in invisible ink and then to write over it again in normal handwriting or as we have discussed, used the larger letters as a guide and written the microcode into them.
The next step would be to remove any indentations from the page beneath and that was done by steaming/iron and water. That didn't happen as is evidenced by the fact that the Police were able to lift the indentations from the inner page and it's those markings that they traced over.
The question is why wasn't the next step taken by the person who wrote the 'code' to remove the indentations by the steam process?
A possible answer is that there wasn't time, so the complete book was grabbed and possibly during an escape the back was torn off and sent in one direction and the rest of the book tossed into an open window of a nearby car hopefully to be collected later.
That could mean that the 'code' was written on SMs last day. It doesn't necessarily follow that it was SM that wrote it. Given this scenario is correct that would make it on November 30th 1948. That may be a date worth bearing in mind as we get on to the Venom or Venona post.