My current costume project is inspired by Pflazagrafin Dorothea Maria Von Sulzbach's gown c1639 as seen in 'Patterns of Fashion The cut and construction of clothes for men and women c1560-1620' by Janet Arnold (PoF). The gown is housed at the Bayerisches Nationalmuseum, Munich.
'Tailors Pattern Book 1589' by Juan De Alcega translated to English by Jean Pain & Cecilia Bainton (Alcega) has patterns that are very similar to this gown. In the Main Notes which can be found at the rear of the book an explanation is given about the difference between a 'Cuera' (main note 36) and 'Sayuelo' (main note 38). Although the cut is basically the same, the 'curea' is an inner garment and the 'sayeulo' is an outer garment. Patterns for 'cuera' also include 'saya', an open fronted petticoat.
Janet Arnold (JA) notes that 'the centre front appears to have been open originally but is now stitched down', which is in keeping with Alcega's curea and saya patterns. JA states that 'Like most elderly people Dorothea Maria probably continued to wear styles which she had worn in middle age and in which she felt comfortable.' This time frame would mean that Dorothea Maria was 30 when Alcega published his pattern book.