Why does this Polish night train have two different numbers?
I'm looking at booking a sleeper train from Szczecin to Warsaw on 9 June 2018, and have found a strange inconsistency in train numbering. On the rail operator's own booking site, https://www.intercity.pl/, the search returns two trains, TLK82172 and TLK82173, whose numbers differ by one. They have exactly the same timings (21:15 - 05:50) so I assume they're the same train, but the TLK82172 is shown as having sleeper cars and the TLK82173 as only having seating.
If I search on any third-party website (https://www.polrail.com/ , http://rozklad.sitkol.pl/bin/query.exe/en , etc.) the TLK82172 doesn't seem to exist at all but the TLK82173 comes up with sleeper cars.
Looking at the Warsaw - Szceczin trip for the same day, the "doubling" doesn't happen: there's just a single TLK28172 which all the booking and timetable websites seem to agree on.
In practice, I assume I'd be safe booking either the sleeper variant of this train at intercity.pl, or the differently-numbered sleeper offered by polrail.com. But for future reference (and slightly more peace of mind) I'd like to know what's going on here: why does this train have two numbers, why don't different websites agree on the numbering or sleeper car provision, and is this kind of thing a frequent occurrence with Polish rail travel?
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