Page 620 - Makino,Tsutusi.DictionaryOfIntermediateJGrammar

II. Nagara also expresses concurrent actions by one person. Thus, nagara
and tsutsu in this use are interchangeable, as in [3].

Note, however, that nagara can be preceded by adjectives and nouns to
express the concurrent states of one entity, while tsutsu cannot, as in
[4]. (Note that de ari in [4b] is the continuative form of the copula de
am.)
pa!.. a%
[41 a. Yk Ci&%jJi.2!$~\ {ah$% / *771 a-n.ts-n.b'b1e~JQ-j-
a 0
(Although Jim doesn't have much experience, he does a
pretty good job.)
+kbixLe
b. @~~Z~)&&~)W.EE%T&~I {&fr'% / *77l ~~9%;k
f 5 2 L-Cb>&o
(Despite the fact that he is the person responsible for this
accident, he is trying to avoid his responsibility.)
Note also that nagara can be preceded by Vneg nai and Vte i while
tsutsu cannot, as in [5].
Cei KL
[51 a. ~~tiS&~~h~~~t\ +D>S-%+~
/*771
CO
% L@f&
(Even though I don't understand English, I could fully
enjoy the show.)

(d nagara(mo) (this volume; DBJG: 269-70))