I have a question for those of you older then me

[GusHerb]

There is a CO by me that was built in 1977, and houses 3 exchanges. Long story short, would that CO have been most likely originally equipped with 1AESS switching equipment?

And another question, does anyone know or can possibly point me toward any kind of documentation of when the RBOC's started using Northern Telecom and Siemen's switches? The only thing I can figure is this was sometime after 1984. The CO I mentioned earlier currently has Siemen's DE4 EWSD equipment and I'm trying to figure a general timeline of when it was upgraded to that, sometime before about 1998 (the earliest I can remember playing with the phone as a child), the recordings, and overall characteristics of the line haven't changed since then.

I have so many questions right now that what I really need is to find an old timer engineer that worked on this stuff in the 70s-90s but I'm sure someone here has an idea.

Thanks guys!

[Weco355aman]

I've been in a lot of Bell System C.O.'s
If the building was built NEW in the 70's it would  have had a 1AESS. If the building was added on to in the late the 70's
it  may have been to add a new switch. There was rarely a time the they would add to a SXS or X-bar unless it was only a few 100 lines. (in large Exchanges) In your small CDO's they would add to the SXS Switches. #5 crossbar systems were very complex and may needed  more common Equipment to support more lines. Step x step was a very simple system to
add on to if needed. SXS could be made into a complex system if it was in a large metro and was also a TDM (tandem).
After the Breakup it was wide open for the RBOC (regional bell operating  company) could buy from any of the Switch Manufactures.
Most of the Bell Company's were majority owned by AT&T and was mostly buying Western Electric Equipment.
Ohio Bell and SNET and a few others was Minority owned by AT&T and was buying a certain % of there items from non WE suppliers
If you see a "KS" listed on a item it was NOT made buy WE but for them. This is a simple answer to a complex Question.
   

[GusHerb]

The building was definitely new, county property records show it as being built 1977, just a small single story building which appears designed only for digital switches. It took over a bit of territory from a much larger CO a few miles away.

When looking up the area CO's I see almost an even sprinkling of Siemen's EWSD, 5ESS, and there appears to be more DMS100's then the other two.
I'm trying to figure things out like the upgrade paths these CO's took (like what came before what they have currently), and why the switches are all mix and matched (like they chose different companies for different phases or something) and when they all eventually got put in.
Like I'm guessing based on my observations that my CO originally with 1AESS was upgraded in the mid 90s to EWSD, while an older CO a few miles away possibly with 1ESS or crossbar got upgraded to 5ESS in the mid-late 80s. I'm kinda just thinking out loud here.