No! Not if we are your supplier.  We only buy first grade, sequentially numbered slabs that have been resined using an epoxy-based resin.
We never cut corners when purchasing slabs.  If a competitor is using, un-resined commercial slabs, or slabs that have been sealed using a polyester based resin, then you will have an issue.  
And, even with epoxy-based resined slabs, we still use a special sealer in the shop prior to installation, and give every customer a spray can of cleaner that contains a small amount of sealer.
We are currently around 4 years of using this methodology and are not being asked to re-seal installed countertops yet.