Old bloomery wrought iron starts out as a bloom that is a pretty nasty mix of iron, slag, ore, furnace wall, fuel, etc. You take that and consolidate it as "Muck Bar". (It can be very mucky---the worst blooms we have worked were consolidated on a wooden stump with a wooden mallet to keep it from "splashing" when hit.) Take several muck bars and forge weld them together and forge them down and you get Merchant Bar; which was what was commonly sold.
If you take several Merchant Bars and stack and forge weld them together and forge out into a bar you get "Singly Refined Wrought Iron" repeat for Doubly Refined and repeat again for Triply Refined Wrought Iron. I've noticed that every culture that used the bloomery method seems to have come up with pattern welding.
Also a lot of scrap Wrought Iron was "busheled" stacked and welded into a recycled bar.
Now later processes didn't do as much "stack and weld" stuff and so doesn't show as much pattern.