What is the origin of the term "back to back", meaning to follow one after the other?

Back-to-front suggests a single item that is the wrong way around or has been reversed, like a shirt with the buttons at the back, or holding a map up the wrong way.

Back-to-back suggests two things touching each other, and unlike in back-to-back housing, the orientation doesn't necessarily matter, especially for abstract terms like agreements and arrangements (in this context).

The phrase "back-to-back agreements" appears to have become prevalent in the early 1970s, but the earliest I found is from this 1956 Petroleum Week:

The other customer-supplier has a "back to back" agreement with Commerce.

However, "back-to-back arrangements" is also synonymously, and also has a slightly older meaning. Here's the 1906 Mineral Resources of the United States

The washing apparatus consisted of a trommel for taking out the coarse material, from which the fines went to two tables with back-to-back arrangements fitted with riffles and mats.

And from a 1933 United States Patents Quarterly:

It is, in effect, only supplying two devices from a common battery, and it was common to do that in these back-to-back arrangements and in carbon buttons for the purpose of getting added sensitivity.

This suggests a similar meaning of next to each other rather than a literal rear-to-rear.

Some houses are built back-to-back, where the back wall of one house is also the back wall of the other. Typically the entire street is like this, so each individual house just has a front of its own, sharing the back and sides with other houses.

Perhaps the general term back-to-back, for a series of things in close succession, comes from these crammed-together dwellings.