GCSEs can be seen as a level 1 qualification, or a level 2 qualification. The only way you can not get either of the qualifications is if you obtain a U grade (Ungraded). Grades 1-3 are classified as a level 1 qualification, while grades 4-9 are classified as a level 2 qualification.
Now, Ofqual's original plan for combined science higher-tier was for the standard to be targeted at grades 4-4 to 9-9. However, there was a caveat. For students that missed the grade 4-4 by a narrow margin, they would obtain a grade 4-3 as a 'safety net' to avoid being graded a U, which Ofqual deemed would have been unfair. However, in light of statistics by awarding organisations, it appears that the country's higher-tier results were so lacklustre for combined science, that not even the 'safety net' grade would prevent a glut of U grades being dished out. The actual reason for this was because teachers had placed students in the wrong tier, and it would be unfair to grade some students who sat the higher-tier a U just because of an error on the teacher's behalf, so a grade 3-3 was introduced as the new 'safety net' for this year to avoid copious Us across the country. The grade 3-3 constitutes as a level 1 qualification, so it is still a GCSE, but not one that's very useful for someone's employability.