Well just about all the legacy boxes were still active on people's systems, but no longer available for purchase nor provided by Dish on new installs by 2002. I know by 2001 I had bought my own 301's, which were fairly cheap price of like $99.00) to replace over a few months those becoming super SLOW to update EPG 2700's slaves (or similar model--2600?) for the upgraded EPG with picture in guide for our bedrooms. It was quite a speedy upgrade that made watching Dish a far better experience.
The living room was a 3900, and my uncle and aunt had gotten the kit from Costco that provided the 4900. Unlike the 3900, the 4900 was capable of RF remote control (and IR), and had an extra set of video/audio outputs, most likely used for a VCR to record programming, and the other set of A/V outputs went to the AV Receiver for the DolbyDigital 2.0/5.1 sound which they had at the time and I did not.
While the 301's RF output was very good, the 3900's output in the living room had a bug that produced a very faint amount of RF noise that drove me crazy, but only a few other people noticed it, as well. I "suffered" the RF output so that the one set of video/audio outputs could connect to the Super VHS VCR's using the SVHS outs from Dish STB. This provided a highly enhanced PQ that for record and playback of all the channels from Dish that, in those days, was very high PQ that was greatly enjoyed in Super VHS with built-in TBC (Time Base Corrector)that cleaned up the VHS shortcomings, for a far better VCR viewing experience that was almost indistinguishable (well, EVERYBODY else could not see the difference) from the original 525 (480 visible) lines of resolution. I think Super VHS was something like 425 horizontal lines of resolution, but the TBC corrected remaining sins of PQ.
I believe the problem with the 2700's and the like PRE DishPro boxes was that Dish had grown its channel offerings tremendously by 2000, and the stream for the EPG was just too long for it to load on those old slaves even though they only showed 48 hours worth of guide data, but there were a heck of a lot of LIL's (hundreds) that were added by then that made it a super long data stream.
Later, instead of using a stream, Dish would send down a highly compressed file that would be loaded/opened locally on the box after the download so the waiting time to load new EPG data was greatly reduced to being not a problem anymore, but not before just about all the Dish boxes were starting to experience the long or failed EPG update around 2002+ years because of the super long data-stream, so the solution came just in time.
I also had the SW64 switch to allow for 4TV's, a rarity in those days. Dish would only subsidize up to TWO TV's--after that, you were on the hook for the extra slaves and other costs--including the pricey SW64. The SW64 could be cranky on rare ocassion, but a quick unplug and replug to power outlet would cure and glitches. Despite its the SW64's moodiness, I LOVED it because it was the only economical way to feed our 4 TV's.
I think the 721 was still in the works by 2002, or more like DELAYED and DELAYED. I forget when it was, finally, released, but I intentionally waited a full year before plunking down the big bucks to get one ($500?) as an owned unit. The 721 was NEVER a subsidized box. After its long delay, Dish started to refer to it as an "enthusiast" model or "power user" model, which seem to make it clear that this box was available at full retail price ONLY! But those who had it, including yours truly, LOVED them. I would dare to only buy ONE of these boxes and let it be used in the living room while I used the 508 in another room, which I got at a subsidized Dish deal of one-time small price. Good heavens! We were overjoyed and felt lucky to have a TWO-tuner DVR, and it really was needed to solve programming conflicts.
Today, the technology changes so fast, I no longer invest much money in tech because its time to move on to the new tech or OS in very little time. A few years pass by very quickly and your model won't support the latest UI or your version of Android no longer supports the apps you NEED, etc., etc.