If 17741 was built in the first week of Jan 74 then Mud would have been built in the last week of December 1973, that's assuming continuous estate production rather than batch production, it may have been built in a batch anytime in late 1973.
What date is your wiper motor? That usually gives a pretty good indication of when the car was built. There will be a bottom row of numbers on it (for example my DL is 51 71 so my wiper motor was made in the 51st week of 1971 and the car was built in the 1st week of 1972- I can say that as we know the last chassis number in 1971). You can also look at the date code on the glass. I don't think glass would have been stored in big quantities for long because of it's fragile nature although it can only be divided into quarters date-wise http://www.mgexp.com/article/triplex-wi ... -code.html
Most cars I have looked at the chassis numbers of seem to have sat for a while before being registered. My DL wasn't registered until May 72, Mossy was built in February/March 72 but not registered until August. My J reg didn't sit for long and went on the road almost fresh off the line. I have one car on the 71 register that has the early wiper pattern but not registered until July 72! TCs and of course Mumfords waited even longer than the regular cars to hit the road. There will be some N and P reg Mumfords that will be tax free now according to Gary Dunster's Mumford register.
