If you're hired for a gig and you played an 11th in a Bb13 chord, you probably wouldn't get called again. The (+11) is most used with a 13th chord. In order to use the natural 11th, the chord would have to be Bb13sus, Bb9sus, Bb7sus. In practical use Bb13 does not include the 11th. There are worlds of difference in what's theoretically correct and what sounds good. Later, Ray

Asus Q500A i7 Win 10 64 bit 8GB ram 750 HD 15.5" touch screen, BIAB 2017, Casio PX 5s, Xw P1, Center Point Stereo SS V3 and EWI 4000s.