Just for the benefit of those who may be confused by terminology used for issuing unit diagrams:
LTP (Long Term Plan) is issued twice a year, May and December currently.
STP (Short term plan) is everything that alters the LTP in any way, and is issued on a weekly basis in essence, and is largely about engineering works and special events (Twickenham Rugby etc).
For larger projects, such as the 701 roll out, there is a further alternative, the PA (Permanent Alteration). These are designed to soak up all the alterations (stock/crew diagrams) involved within that project, and which will eventually become part of the LTP at the next LTP timetable change, be that May or December.
These PA's can be issued once every eight weeks to fall in line with Train crew diagramming rules, so will generally fall (be issued) in February, April, July, September, November (as and when required).
The benefit of PA's is that the changes encompassed within them will be issued just once, before either a further PA (8 weeks later) or they form part of the next LTP (May or December). This frees up the workload of the STP teams, who's time will still be taken up by routine engineering work planning etc, albeit they will still have to refer to the PA's to prevent any clashes during the STP planning process.
So in essence, those new 701 diagrams that are coming to light occasionally, will very likely be a PA issue, the next LTP issue being in May.
Hope that explains the process, and I am assuming it is still essentially the same as in my time!