Rolling Stones Mono Box Set (lp or cd)

Good to see you again- astro58go.  Hope you are enjoying the RS boxed set. Which titles(s) are you completed to date?

When I read this in the original posters start of this thread: 
"One thing that has stood out to me is how consistent these 5 lps are in sound quality."
I immediately suspected that the original recordings probably did not have a consistent sound, and that required the consistency to be a result of audio engineering after the "master tapes."
Let me be clear:  I do not know if my suspicions are true!
But, to make a case, those records were recorded over a period from circa 1964-1970-something? During that period the explosion of record sales feed big changes in the recording studios. 2 and 4 track were common; was 4 track 'state of the art' in the early mid-60's. By 1970 had 8 track recording become more common?
There was probably also a learning curve by everyone involved, from musicians to studio engineers to equipment makers.
I remember reading that The Beatles after a few years and 3 or 4 or LPs told George Martin that they couldn't really hear the Ringo's drums, or bass drums. They thought they role in the recording process precluded them, the musicians reporting to the recording (was Martin the producer--whatever he was) that the sound quality of the recordings was not to their liking.
And we haven't even talked about  mono vs . stereo vs bass before subwoofers. Add up dozens or hundreds of things like that, and I would expect any LP recorded in the UK (and America) in 1964 to sound different than one recorded 5 years later.
Sorry for the long rant.
And Keith Richards is wrong. Srgt Pepper is great. 

drsteve, I had the same suspicions as well. Since I had little to no reference, I chose not to make that statement.

(What low bass that is present on the previous lps is not very musical and artificial sounding.) ( There are a few live recordings peppered throughout, these are of very low SQ.)

I've now listened through December's Children  US/UK - Aftermath US/UK.

The DC sounded just like the previous lps.

"Aftermath"...what I'm now hearing is more pleasing and enjoyable. Wondering if the fact that this lp is the first to have only Jagger/Richards penned songs has anything to do with it. More control over the recording process...?? Better equipment, more knowledgeable in the studio?

There is no longer, the sense of the recording being "too hot". The midrange is more natural and integrated. The mid-bass through low bass is more musical, again better integrated and allows the listener to hear the whole sonic picture....

(drsteve, When I wrote the sentence, "how consistent these 5lps are in sound quality",  I was hoping others would catch on.)

Your explanation of what you think may have been going on during this time in the recordings of these earlier lps is consistent with my own thoughts.

"Between The Buttons". After just hearing "Aftermath", "BTB" is a major disappointment! Partly because of the SQ, but mostly because, IMO, it is a step backwards from their previous effort. The songs are of little importance. This was the time when they were experimenting with overdubs and drugs...The overall effort is inconsequential. This could be considered, the lost RS lp, IMO. The sound is also quite "thin".

Listening to a set such as this in chronological order is very revealing. It gives one a window into what was happening without the benefit of being there.