IIRC items have a default casting level, if not given this can be inferred from the highest level spell used to make it.
This can have unfortunate side effects. One instance I can think of in play was:
A sword that has constant "Light" when drawn, and can do "Sudden Light" 3x/day.
The kinda cool, but not earth shattering low casting level light when drawn effect requires a constant imbed spell, inflating the item to 30+ casting level.
This makes the 3x/day zaps of sudden light, where targets are stunned 1 round per 10% they failed the RR much much nastier, since eating a sudden light at 30+ level was usually enough to stun most opponents for a lot of rounds. . .and is an area effect spell no less.
That'd be fine if said sword were the minor item carried by a 30th level PC, so RRs are scaled to 30th, but as the really awesome item for an 8th level character, it ended up being so game breaking we needed to stop using the "Cast at level needed to create the item" and use another metric. (I think the GM default set the casting level of the sword at 10th level by fiat).