How many variations are there of the Avro Lancaster?
There were twenty-three different variants, according to Wikipedia:

British-built variants (13)


Ten combat variants (B.I, B.I Special, B.I (FE), B.II, B.III, B.III Special, B.IV [Lincoln B 1], B.V [Lincoln B 2], B.VI, B.VII)
Two reconnaissance variants (PR.I, GR.3/MR.3)
One SAR variant (ASR.III/ASR.3)


Canadian-built variants (10)


Two combat variants (B.X [later 10S/10U], B.XV [Lincoln XV])
One dual-purpose combat/reconnaissance variant (10BR)
Three dedicated reconnaissance variants (10AR, 10MR/10MP, 10P)
One SAR variant (10S&amp;R)
One trainer variant (10N)
One drone-mothership variant (10DC)
One jet-engine testbed variant (10O)


Plus the Avro Lancastrian, a commercial airliner derived from the Lancaster B.X (the first few Lancastrians were direct conversions of existing B.Xes, although later batches were built as airliners from the start).