Stanton said the pattern emerged after assessing passenger declaration forms provided by operators.
"They have to do their own incident investigation and what they found was that people knew they had a previous injury to their shoulder but were reluctant to declare it because they thought it would prevent them from jumping."
He said changes to the wording on the passenger declaration form were aimed at encouraging people to disclose medical conditions.
"It needed to be made clear to people that disclosing a medical condition won't prevent them from jumping, but it will allow the tandem master to modify the way he (or she) runs the jump so you don't land on your gammy knee or they don't expose your bad shoulder to the airflow."
The January to March 2020 safety report also showed the overall number of aviation accidents was lower than at the same time last year.
It showed there were 26 accidents in this quarter, compared with the 51 accidents in the same quarter last year.
The nine accidents recorded in the commercial passenger sector were all from adventure aviation passenger operations. There were four accidents in the commercial non-passenger sector (down from 10 the previous year) and 13 in the private and recreational flying sector, which led to one fatality.
There were 28 accidents in the private and recreational sector over the same time last year.
Stanton said the reduction in accidents this year was unlikely to be because of Covid-19 restrictions. The report covered the period from the 1 January to 31 March which covered only one week of lockdown.
He said the reason for the drop was hard to answer because accident investigations focused primarily on causes, rather than what was not a cause.
"The private and recreation area is complex because that's everything from hang gliders to parachutes to small, home-built aircraft - much like recreational boating which has a variety of craft from kayaks to yachts and you have to be careful around saying what the cause was.
"One thing we are seeing a general reduction in recreational flying activity, due to things like rising costs, but the number of accidents have come down faster than the actual activity has reduced."
Stanton said the calmer weather than normal over that timeframe was something they might look into.
"In the past we've found a good percentage of private and recreational accidents are caused by encountering unexpected bad weather, such as flying into rain or cloud so the weather over this time is likely to have a strong co-relation."
Stanton said the aim of the safety reports supported one of CAA's central mission to promote and ensure the safe conduct of air operations.
-RNZ
