Stolen Medicare card number

Can someone kindly explain to me what’s the point of getting a replacement Medicare card after it’s been stolen, other than the fact that you need the card for personal use, when all they do is just change the last digit in a predictable, chronological way ?

Whoever stole the card can still use my ID seeing as he/she just need to change the last number to the next (last digit of the card is 1, then the new card will be 2 .etc)

I don’t understand how this can protect my identity from being stolen ??