In the eighties, there was a vast flowering of small independent software companies. Business and productivity software for the IBM PC, all manner of novelties for the Macintosh, games for the wonderful variety of home computers. In particular, at least on the PC, there were small and medium-sized companies writing original software, and also companies writing bespoke business software on contract; that also happened on mainframes, but for obvious reasons, the minimum size of a mainframe contract programming company is larger than on microcomputers.
There were certainly at least some such companies in the late seventies, e.g. Software Arts, developer of VisiCalc, and for that matter Microsoft, that started off as a small company supplying a version of Basic for the new microcomputers. I have a feeling there were far fewer ISVs in the seventies than in the eighties and later decades, though I don't have statistics.
But what was the situation in the early seventies, the sixties, the fifties? In those days the minimum price of a useful computer was much higher, software was not yet seen as a product in its own right, computers were more likely to be owned by big companies and other organizations that could have their own in-house programming staff, software might even be bundled with rented computers in a scenario where the vendor would not approve of third-party companies doing anything with the machine.
Did small ISVs exist in the era of IBM and DEC, before the rise of microcomputers in the mid-seventies?