The R12 bus has a "Revised timetable for reliability improvements" according to the Salisbury Reds website. *
Could this be useful to you?
The 201 Salisbury to Amesbury bus travels through Stratford sub Castle. According to the Salisbury Reds timetable, on Monday through to Friday, there's a 16:10 bus from New Canal Stop S (and Stop K Tesco Castle Street) that is due at Stratford Bridge at 16:26 - a later departure time than the last R12 bus (14:50).
The timetables below (PDF format) have been downloaded from the Salisbury Reds website:
*Source: Salisbury Reds