The fact that there was only a difference of -61,872 new converts indicates just how many of the newly dedicated people are in-house, many of them being children of JWs who have been brought up in the religion.
ALL newly baptised people are "in-house" because one must attend meetings and serve as an exemplar unbaptised publisher for at least few years (maybe an year or so in some cases) before being baptised.
Newly baptised ≠ new converts.
And I think the 2020 decrease in baptisms can be attributed to "logistics" issues (cancelled assemplies, movement restrictions etc.) rather than to those related to the field ministry.