Goudy686,
Thank you for your insights. I didn't get into firearms until 2008 so I don't have any knowledge or history with items like the internal lock. Thanks again!
No worries, I did not grow up with guns either, and I am far from an expert on most things gun related. The 686 is the one exception, I fell in love with the platform and have dedicated a lot of time learning about my all-time favorite gun. If you ask me about any other firearm I am a novice, it is just the 686 which I am an expert with.
686 (1980): No dash, Begin regular production.
686-1 (1986): Radius stud package; floating hand.
686-M (1987): Recall by S&W and overstamped to indicate a modification by the factory or warranty station; applies to 686 and 686-1 only.
686-2 (1987): Change hammer nose, bushing and associated parts.
686-3 (1988): New yoke retention system.
1990: 2-1/2" barrel introduced.
686-4 (1993): Change rear sight leaf, drill and tap frame, change extractor, introduce Hogue grips.
1995: Introduce power port barrel.
1995: Introduce 7-shot cylinder with seven flutes in 6" barrel length with round butt frame. Serrated backstrap, smooth trigger, 7-point star extractor, RR front sight, service hammer WO rear sight blade, Hogue grips with S&W logo.
1996: Delete square butt; begin shipments in a foam-filled blue plastic case.
1997: Change thumbpiece; ship with Master trigger lock.
686-5 (1997): Change frame design to eliminate cylinder stop stud; eliminate serrated tangs; change to MIM hammer with floating firing pin, change to MIM trigger, change internal lockwork.
686-6 (2001): Internal hammer and trigger key lock.
686-7 (2002): Performance Center variation in .38 Super.
Here is a list of changes made with each generation for your reference. Mine is a -1 modified (M Stamp) to be a dash 2 technically. The inside of the grips will tell you the year mine is 1987, I was born in 1988 so I was one year off from a birth year gun

but I do not get too hung up on that.
The most coveted tend to be the no dash due to being the original and the -4 because it is considered the pinnacle of pre-lock versions. I think they are all great, and even lock versions can be cool, especially the 7 shot ones. Having an extra round of 357 is a phenomenal improvement IMO. The 3 inch 586 pre-lock also tend to be considered pretty rare, I would love to get my hands on one personally as my 4 inch is a little too long for daily carry.
Edit:
Almost forgot to mention the 586 is just the blue version of the 686, and the 3 inch 586 is one of my personal grail guns.