Honestly, I wouldn't worry about it too much.
It's inevitable that over time, your style will evolve, but so long as generally the character retains certain "key identifiers" that are distinct from the other characters in the cast, your audience should always be able to tell which character is which.
The comic I'm currently working on uses a character I've worked with in comics for about sixteen years now, and so inevitably 34 year old me doesn't draw her the same as 18 year old me did. Fashions have changed, my style has changed and I've had years of professional experience, read a lot of books and learned a lot since then... but her key traits always stay the same: Left handed, slightly pear-shaped build, intense green eyes, straight eyebrows, scarlet hair that's very smooth on top then has a spiky fringe, tends to dress in a brash way, has a big heavy anime sword with a brass and red-wrapped hilt.
I think a person would hopefully be able to skip even from the top row to the bottom image and go "Oh yeah, that's the same character" in the same way you can skip from the first pages of longrunning webcomic
Gunnerkrigg Court to the most recent ones and still recognise Annie, even though the style has changed a lot and the character is several years older.
If it helps, make a model sheet that specifically points out and labels the key identifiers of each major character. So long as you include those most important elements of the design, you're usually fine!