Are we assuming the lack of a recorded period is the criteria? If yes, what if you just forgot to add it that month, or have hormonal issues, or abnormal BMI?
Lots of reasons why you would miss a period that aren't pregnancy related. But that's not the point. Missing a period opens you up to further scrutiny and investigation by the state. Now they will start seeing if you've made out of town trips or perhaps subpoena your chat log to see what you've said to friends and family. It's not enough to prosecute, it is enough to start an investigation.
You're welcome to suggest to your lawyer this particular defense.
The people prosecuting women for abortions aren't looking for reasons not to arrest and prosecute them.