Excuse my unresearched answer, but I believe 70 is the point in time when BODs change...I think before 70, you do not get any large bods.
Here it is from this forum's FAQ:
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How often can I get a BOD?
How often you are eligible for a BOD depends on your tailoring skill. From 0.1 to 50.0 tailoring skill the delay is one hour; from 50.1 to 69.9 it is two hours; and from 70.0 to 120 it is six hours. If you select the NPC tailor or weaver’s context sensitive menu s/he will tell you roughly how long you will have to wait before you will be eligible for another BOD. The timer used for tailor BODs is unrelated to the timer used for Blacksmithing.
What kind of BODs do I get at different skill levels?
From 0.1 to 69.9 you will receive BODs that will help you gain tailoring skill when filling them, so you will get normal quality cloth and normal leather BODs. From 70.0 you will receive any kind of BOD: normal/exceptional quality, normal/coloured leather and LBODs.
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