| ante | before |
| dito | same as (with relation to something mentioned previously) |
| ibid. | used to refer to the work cited in the preceding note |
| idem | the same as something previously mentioned |
| ill. | illustrated |
| ms | handwritten |
| n.d. | not dated |
| n.s. | not signed |
| post | after |
| s.n. | no number |
| CORRESPONDENCES | |
| ALS | autograph letter signed |
| ACS | autograph card signed |
| APCS | autograph postcard signed |
| TLS | typed letter signed |
| TL | typed letter unsigned |
| INSTITUTIONS | |
| FdDPS | Endowment Fund Philippe Smit |
| LNC | The Lord’s New Church, Bryn Athyn, PA |
| Glencairn archives | The Bryn Athyn Historic District Archives at Glencairn Museum |
| PMA | Philadelphia Museum of Fine Arts |
| RKD | Rijksbureau voor Kunsthistorische Documentatie (Netherlands Institute for Art History) |