After Trademark regis. you can't add product types?

[HiC]

Looking at the site of the USPTO, they state:

"You must list the specific goods/services for which registration is
sought, regardless of the basis for the application...

....If based on use in commerce, you must already be using the mark in
commerce on or in connection with all the goods and/or services
listed.
If based on intent to use and/or a foreign application or
registration, you must have a bona fide intention to use the mark in
commerce on or in connection with all the listed goods and/or
services...

Can I change the goods and/or services after filing my application?

You can clarify or limit the goods and/or services. However, you may
not expand or broaden the identification of goods and/or services
after filing the application. "

This sounds like once you list whatever products you plan to sell with
a particular business, you're locked into this for all eternity, and
can't add any products or services, yet companies do this all the
time.

Further regarding classifying your goods/services they indicate:

"For a listing of classes, see International Schedule of Classes of
Goods and Services."

But further up they say:

"Please note that the terms in the classification listing of goods and
services in the "International Schedule of Classes of Goods and
Services" are generally too broad and should not be used alone as an
identification."

"For a listing of classes, see International Schedule of Classes of
Goods and Services."

Can anyone provide insight into this?

Thanks!