Hello Viper,
yes, i mean the microvia should be designed on the top of buried via holes B2-3, you know normal huried via holes size is about 0.2-0.3mm, and the microvia holes is around 0.1mm, even if there are some misalignment during drilling microvia , the misalignment is still no more than 0.1mm, and also, buried via holes B2-3 have the responding annular ring , the little clearance will not affect the connection between L1-2 to B2-3.
Since stacked via holes are made normally with laser machine, you know laser is hard to drill the laminate which are thicker than 0.1mm. i have the experience in stackvwillia holes, if you design stackvia holes for a four layers boards, the production cost will be high and the final boards thickness will be thin( about 0.3-0.4mm).
hope you can get my meaning.
Koen.Hu