I mentioned in another thread that there is sometimes an issue with case sensitivity in the Working timetables.
The specific example I was thinking of was for replacement route UL69, where two files have been regularly swapped in and out. The two files are both described on the download page as Schedule_UL69-SSu.pdf. The files are for
(a) SCN 54476 (22nd March 2020), daytype SSu (Summer Sundays)
(b) SCN 58120 (21st March 2021), daytype sSu (special Sundays)
File (b) first appeared in the 23rd March upload, as would be expected.
On 11th May it was replaced by file (a)
On 8th June file (b) took over again
On 29th June it was back to file (a)
This week (6th July) it was back to file (a).
This may be related to the rather wider oscillation bug which seems to have been cured but the case difference provides an added twist.
As it happens, SCN 54476 also has a sSu (special Sunday) file, which looks identical to the SSu. My suspicion is that it always should have been sSu (why would you need a Summer variant ona rail replacement service?).
Whatever, it all comes back to using both s and S as prefixes. I dare say that practice goes back to the dawn of time (or dawn of Windows, perhaps) but it clearly has the capability to confuse.