1) If a woman has been married previously, don't expect all births to the second marriage to have the same maiden name - some may show as her actual maiden name, others may show her previous married name. Could be all one, all the other, or mix'n'match!!

2) Having no maiden name at all (a dash) doesn't necessarily mean illegitimate. It could just mean that whoever registered the birth didn't know it (so where it normally says "Mother: Ann Smith
formerly Jones", then the bit in red isn't there).
For example, the baby may have been born in a workhouse infirmary [maybe just as an "outpatient"] and the master (or whoever) just knew her as Ann Smith