LT1248 is from about 1999
see what looks like a date code at the bottom of the last page
1248fd LT/GP 0799 2K REV D • PRINTED IN USA
i think 0799 is a date, july 1999
package is a 16 pin plastic DIP - an "old" package
see page 6, the section on Pin 6, IAC, at the bottom
L6564 is from about 2013
note copyright on the last page
and date at the bottom of page 1
package is a SSOP10 - a "new" package
I think the difference is that the ST part is newer and has the feature added
to help correct an issue with the older version