Assume our setup is:
M-DD-xxxx, as you're claiming it is.
Now assume scum rolled 3T/4T.
Scum know, after your claim (gee, thanks), that there's only one possible unaccounted for 'x' (M-DD-TTT-x).
Mafia can now safely claim Mason. Why not? By doing so, they're suggesting a setup of MMM-DD-xx. Since a SK in that setup only requires a single T (MMM-DD-T-x), if one exists he wouldn't be particularly suspicious as there's still one unclaimed letter.
Now, because there are multiple Doctors in the setup, scum can play around with when and whom to kill. Based on any additional claims they can determine if they're really 3T or 4T (and thus if there's a SK). Further, they don't even draw THAT much suspicion by not dying right away because there's at LEAST two other targets they could choose to shoot first. Add in any other claims, and they possibly have 3/4 other people to shoot.
And lastly they can argue that scum is choosing not to kill them to frame them.
So "Masons", should not claim at this point. I haven't even considered if you're lying scum who wants his scum buddies to claim Mason yet.
Regardless, no claims. They DON'T narrow the lynch pool and they DO give scum more information.