Programming style evolves over time
I could draw (paint?) analogies between programming and being a painter (for example). Art historians can identify painters by characteristics of a painting, including how a painter's style evolves over a period of time. There are problems with attribution though with students of a painter adopting similar characteristics as their tutor, and the input that students have of helping the master with the incidentals of a work of art (e.g., Gainsborough getting his assistants to do the landscape background while he concentrated on the portrait). Then there are new techniques: new types of paint and canvas (Hockney moving from conventional canvas to photographic collage and then to tablet being a good example) which necessitate a change in style - analogous to a new or updated programming language installed on a different pc or with a different targetted platform.
As mentioned earlier Stack Overflow copy and paste is an example of how things change in the programmer's world. A piece of coding that is homogenously constructed, sporadically interspersed with anachronistic styles where sites such as Stack Overflow have been dipped into for inspiration. Then future works by the same programmer where those code snippets are bedded-in to the coder's customary style.