It is possibilities like the one you posted among other things that make me vary of just calling the whole thing a fraud. In the end it may be that the 7s 6d actually strengthens the likelihood that the document is genuine.
There is - or at least was - so much "arcana" in British (and Imperial) legal and administrative routines that unless you are an expert on these issues it is very easy to come to the wrong conclusion.
BTW did you know that for a short time there was an English coin 7s 6d ? It was called the Angel. The value of the coin varied throughout history (6s 8d) when it was introduced in the 14th century and 11s when it was last coined during the English Civil War.
However, the Angel was an iconic coin and though it hasn't been in use for more than 400 years the name still lives on in the names of pubs and underground stations.
This is why I love FR.
Thanks!