As I understand it, the ages correspond to an "ideal" column that is supposed to be more or less uniform around the planet although intact only in scattered fragments. So whatever layer happens to be exposed is not going to change the order or the age assigned to it.
Within this web site is a list of 25 places on Earth where the entire geologic column exists without interruption (discontinuity) from the Precambrian (older than 570 million years) to the present.
http://www.talkorigins.org/faqs/geocolumn/
While this may not exactly be a favorite website for YECs, it does include several references which may be traced for further information.
Any ideal column is imaginary, since there are 25 real ones going back over 570 million years. Naturally, they do not have exactly the same type of rock at the same place in the columns from one end of the Earth to the other, as depostional environments were different in different places on the Earth. For example, a deep water deposit in a then submerged part of what is now North America may deposit shale, an alluvial streambed in Africa may deposit a congomerate, a shallow sea in Antartica may deposit limestone, and a windblown plain in Asia may deposit sandstone, all at exactly the same time. It is the relationship between strata, including fossils, that helps determine age (among other things). Because depositional environments differ, there is no ideal geologic column.
The geologic time scale
Geologic time scale - Wikipedia is a human construct derived from thousands of wells and field surveys. It is a result of the human need to categorize a continuous phenomena into discrete parts in order to facilitate communication.
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