Sometimes a tampo operation is missed out simply because the ink ran out during the tampo print production run. Several dozen may have passed through the run before, if at all, it was noticed that the ink plate well was dry. Even if noticed the production official may have turned a blind eye rather than re-run dozens or hundreds through the tampo print machine again.
However, many productions runs of cars for Sets did have reduced printing operations on them to reduce cost. Given that Paul Atkin’s and Adrian Leggett‘s cars have both been identified, I think we’ll classify this as a variant. So, in any event it is a factory variation, with the Castrol logo missing from the front edge of the side pods. C2161W Type 3 is now recorded.