I checked the Bell System history. Here's the deal on 1+.
Extending the switch train in SxS to handle ten digits would've been too expensive. Instead users dialed first dialed 112 which connected them to a toll switch that received the extra digits. Later 112 was changed to 1 as SxS was changed from 11n to n11 for service codes.
Originally, SxS users _may_ have had to wait for a second dial tone from the toll switch. (I believe I've seen directions in phone books to do so). Later they had a high speed "bylink" which allowed straight dialing. The toll switch might have been a crossbar tandem. While the #4 crossbar was the bulk of the DDD network, SxS tandems also were important in short-haul long distance.
One challenge in toll switching was the variety of inter-switch dial protocols--direct pulses, MF, PCI, etc. There was also a variety of trunks, e.g. two-way and one-way, two-wire, four-wire. One function of the toll switch was to add balance/repeater "pads" to the connection as dictated by the routing. This was tricky since the wrong setup would give a lot of echo. I recall Directory Assistance long distance had bad echo, perhaps they recognized it was a free "special" call and didn't bother padding it as they would a 'real' call. (Echo is a problem I have to this day on my cell phone occassionally.)
The 1+ was also used as a "toll barrier" in some states. We had 1+7d for short haul toll calls.
#5 crossbar was designed from the beginning to be able to handle ten digits.
Panel and #1 crossbar did not have the capacity. An add-on auxillary sender had to be developed for both of them. When the switch detected an area code to collected 8 digits then sent them out, using PCI, to the auxillary sender, which then accepted the last 2 digits directly.
Panel switches got rebuilt to reflect the numerous modifications made to them over the years.
When we read about all the considerations necessasry to make DDD work, the effort is all the more impressive. It was far more than merely dialing through national switches. There was need to connect between many disaparate signalling arrangements from the sending and receiving office (which included Independent companies with their own protocols). There was also the need for accurate supervision and billing.
I don't know the exact proportions, but my guess is that the big cities got DDD between 1960 and 1965 and the rest of the Bell System mostly between 1965 and 1970. Obviously some places got it much earlier (in the 50s) and others later.
In the early 1960s they sought to automate operator handled calls (coin, credit card, collect, person, etc.), which accounted for 40% of the traffic. TSP/TSPS were developed to handle that. I've read that some cord boards were augmented with a computerized assist, kind of a poor man's TSP, while the operator made the connection in the traditional way, she had a keypad and some indicator lights and could key in the billing data instead of encoding a ticket. I suspect that system saved a lot of time. (Somebody's website out there describes this).
Also, TSP operators had a liberal supply of charge tickets and apparently made good use of them in case the AMA failed or was not usable for some reason.
As to charge tickets, the Bell System made good use of "mark sense" cards, in which they used a #2 pencil to fill in circles. An IBM machine then 'read' these and punched out the data automatically. While this saved keypunched, I think it must have been noticeably slower for the operator to fill in the circles (I always hated doing that) than if they merely wrote down a number. The above mentioned computer augmentation undoubtedly was far more productive.[public replies, please]