How to tell for sure if paint is eggshell or gloss?
One paint company defines the various finishes as follows:


  
  Satin: A finish with a low luster appearance. Washable surface, reflects some light.
  Semi-Gloss: A finish that has noticable gloss and sheen. Washable, sometimes scrubbable surface, but shows surface
  imperfections. Reflects light noticeably
  Eggshell / Low Gloss: A finish ½ way between satin and semi-gloss with a noticeable gloss and sheen. Washable, sometimes
  scrubbable, but may show surface imperfections. Reflects light
  noticeably.
  Gloss: A finish with a high degree of gloss and sheen. Scrubbable surface imperfections. Reflects light very well. If
  properly applied almost gives the impression of ceramic or glass
  finish.
  
  
  They also explain gloss and sheen:
  
  
  Gloss: Measured at a 60° angle, it's the shininess or reflectiveness of a coating.
  Sheen: Measured at an 85° angle, it's a moderately low degree of gloss that appears flat when viewed near or perpendicular, but
  glossy when viewed from a low or sharp angle.
  


There is no industry standard for paint sheens, so one company's eggshell can be another company's satin, matte or low gloss.