Both. Lucky and Experts Wrong
The buss has two purposes. One is to provide ample power to remote sections, two to ensure the signal reaches all areas.
Rail joints are the bane of both DCC and DC. Your joints must be tight otherwise you would lose power and signal. Evidently your track joints must be tight or soldered.
Under DC operation it was one loco per block. The typical single DC pack was ample.
With DCC there are many locos per block requiring more amperage than typical rail joints can carry. That’s where the buss and jumpers come into play. The buss is usually a heavy gauge and resupplies or supplies power to the tracks beyond the capability of the rail joiners.
You probably did not operate more than one to three locos at a time so the basic DCC system provided enough power and it satisfactorily reached all points. Even if there was a voltage drop it would not affect your operation. Typically we do not operate with 12 volts supplied to the motor. So long as track voltage remained higher than the operating voltage you did not notice the difference.
If you are satisfied with the operation of the old section leave it as is. Or maybe hooking up the jumper at the furthest track. But definitely run the new section from the buss or from a booster.
On Behalf Of george
Just a comment . . . And much to my surprise, a true story.
A couple years back, I started a new layout and made the decision it would DCC throughout. It's relatively small, a HO double deck plan in 12' x 14' extra bedroom. I studied all the files, went to DCC clinics at a number of conventions, and built the layout using the recommended wiring practices.
Upon completing the track work, which includes a twelve track fiddle yard, multiple DCC friendly turnouts, cross-overs, and sidings, I was tickled pink that first train navigated every inch of track without so much as a hiccup.
Jump ahead a couple of years and I'm facing an expansion of the layout into an adjacent room. A review of the wiring was needed and during that exercise I discovered I did not complete all the recommended wiring practices, as stated by "the experts" from a couple of years back.
My discovery? Well, much to my surprise (even though the entire layout had a main power bus under every foot of length) . . . There was only ONE pair of track feeder wires powering the entire layout! One and only one. Two years of running multiple trains and never a power problem.
We're the experts wrong? Or was I just lucky? Or what? I doubt a specific answer will ever present itself, and I'm sure there will be opinions galore.
As for me and the layout and the discovered omission . . . I say I'll let this sleeping dog rest where he is and do nothing to upset him.
My conclusion to all of this discussion is this . . . DCC is the simplest wiring required for any model railroad. As long as you don't over think it. Like they say, "KISS!"