The following is the tailor BOD point progression, without the current random bonus points...
Less than 50 / Cloth Group 1 100%
50 to 99 / Cloth Group 2 100%
100 to 149 / Cloth Group 3 100%
150 to 199 / Cloth Group 4 90% Colored Sandals 10%
200 to 299 / Cloth Group 5 80% Colored Sandals 20%
300 to 349 / Stretched Hide 100%
350 to 399 / Spined Runic Sewing Kit 100%
400 to 449 / Tailoring Power Scroll +5 40% Tapestry Deed 60%
450 to 499 / Bear Rug 100%
500 to 549 / Tailoring Power Scroll +10 100%
550 to 574 / Clothing Bless Deed 100%
575 to 599 / Tailoring Power Scroll +15 100%
600 to 649 / Horned Runic Sewing Kit 100%
650 to 699 / Tailoring Power Scroll +20 100%
700+ / Barbed Runic Sewing Kit 100%
As you can see, a bonus of 50 can turn a CBD or PS 115 LBOD into a horned kit, a PS 120 scroll into a Barbed kit, or (maybe*) a PS 110 into a CBD. BUT, by the same token, it will probably turn a Horned kit into a 120 PS.
As we have seen evidence of bonuses turning Horned kit BODs into either 120 PS OR Barbed Kits, we can only assume that sometimes the bonus is around 50 points, other times it is around 100 points.
We do not know yet if the bonus is totally random, tied to the character somehow (skill, age, etc.), or what. We also don't know at what level bonuses actually start being applied (hence the * for MAYBE a PS 110 getting boosted - not seen anyone do those enough), though tests so far would seem to indicate that a BOD has to have a minimum point value above a certain point to have a chance for a boosted level.
The Following is the smith chart...
Less than 25 / Sturdy Shovel 100%
25 to 49 / Sturdy Pickaxe 100%
50 to 99 / Sturdy Shovel 45% Sturdy Pickaxe 45% Leather Gloves of Mining +1 10%
200 to 399 / Gargoyle's Pickaxe 40% Prospector's Tool 40% Studded Gloves of Mining +3 10%
400 to 449 / Gargoyle's Pickaxe 40% Prospector's tool 40% Powder of Temperment 20%
450 to 499 / Powder of Temperment 90% Ringmail Mining Gloves +5 10%
500 to 549 / Dull Copper Runic Hammer 100%
550 to 599 / Dull Copper Runic Hammer 60% Shadow Runic Hammer 40%
600 to 624 / Shadow Runic Hammer 100%
625 to 649 / Shadow Runic Hammer 30% Blacksmith Power Scroll +5 60% Hued Anvil (random hue) 10%
650 to 674 / Copper Runic Hammer 100%
675 to 699 / Hued Anvil (random hue) 10% Blacksmith Power Scroll +10 60% Copper Runic Hammer 30%
700 to 749 / Bronze Runic Hammer 100%
750 to 799 / Ancient Smithy Hammer +10 100%
800 to 849 / Blacksmith Power Scroll +15 100%
850 to 899 / Ancient Smithy Hammer +15 100%
900 to 949 / Blacksmith Power Scroll +20 100%
950 to 999 / Golden Runic Hammer 100%
1000 to 1049 / Ancient Smithy Hammer +30 100%
1050 to 1099 / Agapite Runic Hammer 100%
1100 to 1149 / Ancient Smithy Hammer +60 100%
1150 to 1199 / Verite Runic Hammer 100%
1200+ / Valorite Runic Hammer 100%
While most reported boosts have been 50 points, there have been some of as much as 200 points, reported for smiths. All while still potentially getting the original reward as well.
Until the devs actually fess up to the EXACT process going on, all the rest of us can do is see the occasional results, and GUESS at what is going on.