There's an acquisition history included in the attachment, and I'm not sure how exhaustive it is, but based on reviewing it, I would disagree that they started buying software businesses in the early 2000's in any material way. I would say that they have been buying software businesses as a primary focus since maybe 2009-2010. And looking back at their historical P/S, the P/S ratio has been steadily increasing since around that time from 3x sales to around 5-6x sales now.
Here's a full list of all M&A activity to date -- sorry for the small print. Looks like there were doing some smaller deals in 2001 time frame. To be fair, it was not disclosed how large those deals were. You can also look at old transcripts to get a sense of their thinking back then. For example, from 1q05: "I think what is attractive is capturing the customer and being able to get the recurring revenue from the technology sales, which are high margin, and then trying to win the full scope of services."
Edit: Full software M&A to date, apologies 20200430_015449262PM_Deal_Summary_ROP-US.pdf