If you get data in a weird format, don't let that mistake propagate into your app. 

For example, I once worked on a legacy system that received data from an external source in a CSV file. Dates in this file were, split into three columns: day, month and year.

Surprisingly this had led the system's designer to store dates in the database not as date values, but as three columns: day, month and year. The result of course propagated to the whole system so that every place dates were used they were three separate values instead of a semantically meaningful atomic DateTime class.

Needless to say this caused all kinds of problems around the system.

The lesson is very clear - and particularly something you need to observe at interfaces and system boundaries:

Don't propagate a bad decision.

Create a model that is semantically correct according to the business domain and implement a mapping at the interface points.