1974 D Quarter More Errors

While it isn't impossible for this to happen, it is a vanishingly small occurrence, especially in a coin so well circulated. Much more likely (and true in this case) is that the heavy circulation wear and random damage has caused these sorts of unusual aspects.

First off to CCF

So, when it comes to a filled mint mark...just throw that out a window...they are very common on all years and adds no value nor collectible...only place they are valuable are on other sites for views, likes and follows.

The spitting eagle is know as a die clash, although yours appears to be ones from the photos it could be a scratch. You could look further into it at mad die clashes.com

Squashed lettering just looks like wear and tear to me...remember the year of the coin when examining it. This quarter has been out there working for over 50 years.

Good luck on future finds and keep asking ....