user: Question: How many series originally aired before 1999 with more than 7 episodes and a DVD Region 1 release date of 16 april 2013?
Columns: ['Series Number', 'Number of Episodes', 'Original Air Date', 'DVD Region 2 release date', 'DVD Region 1 release date']
Types: ['real', 'real', 'real', 'text', 'text']
Sample row: [1.0, 6.0, 1973.0, '2 September 2002', 'TBA']
SQL:

assistant: SELECT COUNT("Series Number") FROM "Table" WHERE "Original Air Date" < 1999.0 AND "Number of Episodes" > 7.0 AND "DVD Region 1 release date" = '16 april 2013';