The numbers 42, 43 and 44 have a long history in the Petty Organization. The number 45 that Kyle has been using was to be the number for Adam so it could not be used to add recognition to the new team but the 44 could.
Actually the #44 did not have a long history with the Petty Organization, that number only came into play the year after Richard retired, with the main car carrying that number instead of the #43 for the first year after the retirement.
The storied history of the Petty Organization during the "Glory Days" the numbers most often used were the #s 41-43 With 41 being the non family member number, Jim Pascal drove that car for a few years,#42 being the original number of Papa Lee Petty and we all know who used the #43.
The #45 came into play for Adam as being a number that would be associated with Adam and not a hand me down number. Kyle did start using it after Adam died as a tribute to his late son.
I believe the reason for the #10 being switched to #44 was just for number connection, so that the team could be #9 and #19 then #43 and #44, this would be easy association for the four cars.
Now for my last soapbox statement, I say put the #3 on another car, there is no magic in that number and to place that number on some high level as to make untouchable is throwing dirt in the face of every other driver to drive and die in NASCAR. If you are going to allow the #3 to be not used then pull the #8 and #7 as both were numbers that champions had who died defending their championships. Next you must look at #71,#22 and of other numbers that were on the doors of cars in which Cup drives were killed in. Come on people Sr. was a great driver, but isnt eight years enough time to honor a driver by making that number more than it is?