Gulp task multiple and shared scss files

In my current project, I have three main .scss files. Each one of them imports a lot of partials files, and sometimes, a partial files is imported in two or three of the main files.

For example: I have a main.scss and a nl-main.scss files. main.scss imports the partials _page.scss and _post.scss. nl-main.scss imports _title.scss and _post.scss. Here is my current folder structure:

css
   modules
      _page.scss
      _post.scss
      _title.scss
   main.scss
   nl-main.scss

And here is my current gulpfile.js setup:

var gulp = require( 'gulp' ),
        sass = require( 'gulp-sass' ),
        autoprefixer = require( 'gulp-autoprefixer' ),
        minifycss = require( 'gulp-minify-css' ),
        uglify = require( 'gulp-uglify' ),
        rename = require( 'gulp-rename' ),
        clean = require( 'gulp-clean' ),
        concat = require( 'gulp-concat' ),
        plumber = require( 'gulp-plumber' ),
        notify = require( 'gulp-notify' ),
        projectTitle = 'Project Name';

// styles task
gulp.task( 'styles', function() {
    return gulp.src( 'src/css/main.scss' )
        .pipe( plumber() )
        .pipe( sass({ paths: ['src/css/'] }) )
        .pipe( notify( {
        title: projectTitle,
        message: 'File: <%= file.relative %> was compiled!'
        } ) )
        .pipe( autoprefixer( 'last 2 version', 'safari 5', 'ie 8', 'ie 9', 'opera 12.1', 'ios 6', 'android 4' ) )
        .pipe( gulp.dest( 'dist/assets/css' ) )
        .pipe( rename( { suffix: '.min' } ) )
        .pipe( minifycss() )
        .pipe( gulp.dest( 'dist/assets/css' ) )
        .pipe( notify( {
        title: projectTitle,
        message: 'Minified file: <%= file.relative %> was created / updated!'
        } ) )
} );

// styles task - not logged
gulp.task( 'nl-styles', function() {
    return gulp.src( 'src/css/nl-main.scss' )
        .pipe( plumber() )
        .pipe( sass({ paths: ['src/css/'] }) )
        .pipe( notify( {
        title: projectTitle,
        message: 'File: <%= file.relative %> was compiled!'
        } ) )
        .pipe( autoprefixer( 'last 2 version', 'safari 5', 'ie 8', 'ie 9', 'opera 12.1', 'ios 6', 'android 4' ) )
        .pipe( gulp.dest( 'dist/assets/css' ) )
        .pipe( rename( { suffix: '.min' } ) )
        .pipe( minifycss() )
        .pipe( gulp.dest( 'dist/assets/css' ) )
        .pipe( notify( {
        title: projectTitle,
        message: 'Minified file: <%= file.relative %> was created / updated!'
        } ) )
} );

// watch task
gulp.task( 'watch', function() {

    // Watch .scss files
    gulp.watch( 'src/css/**/*.scss', [ 'styles', 'nl-styles' ] );

});

But, when I run gulp watch, only the nl-styles task runs.

My question is what's the best approach to make this work and runs both the tasks (or only one task, if no shared partials are modified)? Any tips on this?

Thanks!