Why NSS version of curl is different from nss rpm?

Issue

• Why NSS version of curl is different from nss rpm?

The following sample shows NSS/3.15.3 with nss-3.16.1-7.el6_5.

# curl -V | grep NSS
curl 7.19.7 (x86_64-redhat-linux-gnu) libcurl/7.19.7 NSS/3.15.3 zlib/1.2.3 libidn/1.18 libssh2/1.4.2
# rpm -q nss
nss-3.16.1-7.el6_5.x86_64

phpinfo() shows the same versoin.

# cat /etc/php.d/curl.ini
; Enable curl extension module
extension=curl.so
# php -i 2> /dev/null | grep NSS
SSL Version => NSS/3.15.3