[FastJack]

As a point it is usually stated the latest printing of rules superceeds old rules to which Street magic is older than the new SR4a

Good call Casazil. SR4a would trump Street Magic, so is Stacking foci still possible?

[Casazil]

I didn't see anything in the SR4a so now it is an issue of did they negate a whole idea from street magic or is the rule in SR4a incorrcet? this now is the domain of someone like Jason...I would think.

[FastJack]

Agreed, the nebulous area that Street Magic is 'Advanced Rules' makes it seem like it would still be in effect, and I'm not sure when the Errata for it (v1.4.1) was last updated.

[Mäx]

As a point it is usually stated the latest printing of rules superceeds old rules to which Street magic is older than the new SR4a

Thats mostly for printings of the same book or for situations where 2 books have different rules for the same think.
SR4A doesn't have anythink on stacked foci, so the rules from Street magic ably.

[Casazil]

I would guess this is what an offical answer would say too.