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Logical Channel Numbers are assigned by the platform, not carried in the transmission, which is why they differ between nations and why a retune can move them.
Channel number	Where that number applies	Multiplex	System	Format	Availability
49	everywhere it is carried	PSB2 (D3&4)	DVB-T	16:9 SDTV

On PSB2 (D3&4)

1,127 transmitters radiate PSB2 [V] — nearly every television transmitter in the country. By nation: England (638), Scotland (236), Wales (205), Northern Ireland (48). It is operated by Digital 3&4 (ITV/Channel 4).

If this is missing, so is everything here

16 other services share PSB2. A multiplex is one 8 MHz transmission carrying all of them at once, so it arrives whole or not at all — losing exactly one of these and keeping the rest is a fault in the channel, not in your reception.

ITV1 / STVChannel 4S4C5ITV2ITV3E4Film4Channel 4 +1More4ITV4ITV QuizE4 +1ITV1 +1 / STV +1That's 20th CenturyFreeview

Which multiplexes should reach a particular address is the postcode lookup.