Perhaps it was just a dislike of Adalbert? My gt. grandmother appears to have been Mary Jane, cannot find any record of marriage so have no idea what she married under and consequently cannot trace birth, but the two closest guesses have her as Mary. Three children's births were registered, on all she is plain Jane as she is on husband's death certificate. Then she never appears as Jane again but is recorded several times officially as plain Mary. On her death certificate she ends up as Mary Jane. Your guess is as good as mine - I have a feeling her husband did not like Mary and preferred calling her Jane, she adored him and when he died she did not want anyone else to call her Jane. Just to show what can happen - hope it helps.